Molecular sieve materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Molecular sieves that find application in catalysis include any of the naturally occurring or synthetic crystalline molecular sieves. Examples of these zeolites include large pore zeolites, intermediate pore size zeolites, and small pore zeolites. These zeolites and their isotypes are described in “Atlas of Zeolite Framework Types”, eds. W. H. Meier, D. H. Olson and Ch. Baerlocher, Elsevier, Fifth Edition, 2001, which is hereby incorporated by reference. A large pore zeolite generally has a pore size of at least about 7 Å and includes LTL, VFI, MAZ, FAU, OFF, *BEA, and MOR framework type zeolites (IUPAC Commission of Zeolite Nomenclature). Examples of large pore zeolites include mazzite, offretite, zeolite L, VPI-5, zeolite Y, zeolite X, omega, and Beta. An intermediate pore size zeolite generally has a pore size from about 5 Å to less than about 7 Å and includes, for example, MFI, MEL, EUO, MTT, MFS, AEL, AFO, HEU, FER, MWW, and TON framework type zeolites (IUPAC Commission of Zeolite Nomenclature). Examples of intermediate pore size zeolites include ZSM-5, ZSM-11, ZSM-22, MCM-22, silicalite 1, and silicalite 2. A small pore size zeolite has a pore size from about 3 Å to less than about 5.0 Å and includes, for example, CHA, ERI, KFI, LEV, SOD, and LTA framework type zeolites (IUPAC Commission of Zeolite Nomenclature). Examples of small pore zeolites include ZK-4, ZSM-2, SAPO-34, SAPO-35, ZK-14, SAPO-42, ZK-21, ZK-22, ZK-5, ZK-20, zeolite A, chabazite, zeolite T, gmelinite, ALPO-17, and clinoptilolite.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline molecular sieves, such as crystalline silicates. These silicates can be described as a rigid three-dimensional framework of SiO4 and Periodic Table Group 13 element oxide, e.g., AlO4, in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total Group 13 element, e.g., aluminum, and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing the Group 13 element, e.g., aluminum, is balanced by the inclusion in the crystal of a cation, for example an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of the Group 13 element, e.g., aluminum, to the number of various cations, such as Ca2+/2, Sr2+/2, Na+, K+ or Li+, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given silicate by suitable selection of the cation.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. Many of these zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite A (U.S. Pat. No. 2,882,243); zeolite X (U.S. Pat. No. 2,882,244); zeolite Y (U.S. Pat. No. 3,130,007); zeolite ZK-5 (U.S. Pat. No. 3,247,195); zeolite ZK-4 (U.S. Pat. No. 3,314,752); zeolite ZSM-5 (U.S. Pat. No. 3,702,886); zeolite ZSM-11 (U.S. Pat. No. 3,709,979); zeolite ZSM-12 (U.S. Pat. No. 3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983); ZSM-35 (U.S. Pat. No. 4,016,245); zeolite ZSM-23 (U.S. Pat. No. 4,076,842); zeolite MCM-22 (U.S. Pat. No. 4,954,325); and zeolite MCM-35 (U.S. Pat. No. 4,981,663), merely to name a few.
A summary of the prior art, in terms of production, modification and characterization of molecular sieves, is described in the book “Molecular Sieves—Principles of Synthesis and Identification”; (R. Szostak, Blackie Academic & Professional, London, 1998, Second Edition). In addition to molecular sieves, amorphous materials, chiefly silica, aluminum silicate and aluminum oxide, have been used as adsorbents and catalyst supports. A number of long-known techniques, like spray drying, prilling, pelletizing and extrusion, have been and are being used to produce macrostructures in the form of, for example, spherical particles, extrudates, pellets and tablets of both microporous and other types of porous materials for use in catalysis, adsorption and ion exchange. A summary of these techniques is described in “Catalyst Manufacture,” A. B. Stiles and T. A. Koch, Marcel Dekker, New York, 1995.
Numerous methods have been developed to increase the activity of catalysts. Molecular sieve acid activity can be increased by various means such as mild steaming, hydrothermal treatment in the presence of aluminum, and vapor phase treatment with aluminum chloride. Various chemical treatments of molecular sieves have been proposed to modify their chemical properties and increase catalyst activity. U.S. Pat. No. 6,124,228 teaches a standard method of increasing catalyst activity by performing an ion exchange with an ammonium salt followed by calcination. The activated or acidified form of the molecular sieve is often referred to as the H-form molecular sieve or the proton form of the molecular sieve.
Many as-synthesized molecular sieves contain cations, such as, sodium and/or potassium, which are chemically bonded to the molecular sieve framework. In addition, the as-synthesized molecular sieve may comprise salt, such as, sodium hydroxide, which is chemically bonded to the molecular sieve framework. Conventionally, the as-synthesized molecular sieve is converted to its proton form that normally exhibits catalytic acidity for acid catalyzed reactions by ammonium ion exchange of the as-synthesized molecular sieve with an ammonium salt, e.g., ammonium nitrate, ammonium sulfate, or ammonium chloride, to form an ammonium-form (NH4-form) molecular sieve. The ammonium-form molecular sieve is then calcined in N2 and/or air at a suitable temperature to decompose ammonium to ammonia and proton, which forms the proton-form molecular sieve. The conventional ammonium ion exchange process generates a waste stream containing nitrate, sulfate, or chloride. There is, therefore, a need for a novel and environmentally friendly process of making ammonium-form molecular sieve.